1. Field of Invention
This invention relates to the construction of a robust, high conductivity, inexpensive, easy to assemble and serviceable battery contacts for cylindrical battery cells. These battery contacts can be used repeatedly on a printed circuit board to form a larger battery module. Battery modules can be combined to form a larger battery pack. The high conductivity battery contacts allow the utilization of high energy density battery cells such as lithium ion cylindrical cells for high power applications. These battery packs have numerous applications such as electric tools, energy storage and electric vehicles.
2. Discussion of Prior Art
Recent advances in batteries based on lithium chemistries have led to the development of small batteries with extremely high energy density. Unfortunately the inherent thermal stability problems associated with lithium based chemistries severely limits the size of these batteries. The safest and most common lithium based batteries are the lithium ion cells which are available in a small cylindrical form.
There are many devices, for example electric vehicles, that require large stores of energy for electrical power. To address these needs, conventional approaches create a battery pack out of many individual smaller cells and electrically connect them in both series and parallel. This configuration typically produces a desired combination of output voltage and current. In many configurations using this approach, hundreds or thousands of cells may need to be connected together in order to achieve the desired combination of capacity, output voltage and current. This task of assembling large quantities of cells together in a robust and economical way is a new challenge that is not adequately solved by conventional assembly methods.
Manufacturing battery cell assemblies requires significant care and precision in order to create a viable product. For example, with respect to these traditional assemblies, cells are electrically connected to each other by permanent cell tabs. These cell tabs are typically made from thin strips of nickel or stainless steel. The cell tabs are connected to each cell by either spot welding or soldering. The cell tabs must be thin enough to weld to the cell without damaging the cell from excessive welding or soldering heat. In addition, most battery cells, particularly those based on lithium chemistry, are very intolerant of heating. Overheating these types of cells damages the cell chemistry. The result is reduced cell capacity to store energy or premature cell failure.
As for applications of the battery cell assemblies, many devices such as electric vehicles require large amounts of peak current. Thus, each cell tab must be large enough to carry this heavy current load. The nickel alloy typically used is only one fifth the conductivity of copper so the size of the tab must be many times larger in order to have equivalent resistance. Unfortunately, these large interconnects are difficult to weld or solder to the cells without damaging them. Moreover, a reliability problem arises when using large interconnects because they are stiff. The stiff interconnects do not allow for minute cell movement that might occur during thermal expansion or vibration.
Serviceability of the battery pack is also an issue. A pack assembled with all welded construction cannot easily be dissembled in order to replace a cell. It is also difficult to assemble large clusters of cells that have been welded together due to their weight, bulk and fragile connections.
Placement of auxiliary components such as fuses, temperature sensors and temperature cutoffs are also a problem. When these components are wired to lengths of insulted wire, they become cumbersome and difficult to install or remove for service. A typical battery pack is covered with complex runs of electrical wires. Routing and maintaining all of the wires makes assembly difficult and expensive.
When only low conductivity battery contacts are required, there are numerous designs that utilize steel or steel alloy springs for the contacts. This is the common battery contact found in most battery devices such as flashlights. The functionality and serviceability of these contacts is excellent, but there are no designs that can handle high current.
Thus, there is lacking, inter alia, a battery cell assembly that allows for high current carrying capacity, robust construction with flexibility, cost effective manufacturing, ease of assembly, structural integrity, serviceability and a reduction in the number of failure points within the assembly.